1. Field of the Invention
The invention pertains to an efficient method for producing levoglucosan as pure, white crystals, and more particularly, an efficient method for isolating levoglucosan in a highly pure crystalline form by treating pyrolysis oil derived from cellulose with water and an excess amount of a basic metal salt to form a slurry; drying the slurry azeotropically with methylisobutyl ketone solvent to form a residue and drying the residue; grinding the residue to a powder; continuously extracting the powder residue with ethyl acetate to provide a levoglucosan-rich extract; and concentrating the extract by removing ethyl acetate to provide crystalline levoglucosan.
2. Description of the Prior Art
In efforts to manufacture conventional wood adhesives from renewable resources, instead of petrochemicals, methods have been investigated for converting levoglucosan into components of fast-curing adhesives.
Unfortunately, however, as presently available, pure levoglucosan is very expensive. Further, presently known processes for providing levoglucosan give levoglucosan in a form that is contaminated by impurities, such that levoglucosan is not inexpensively and simply provided as a white crystalline material of high yield and high purity when using these processes.
A cellulose-derived pyrolysis oil from which levoglucosan is derived is subjected to an extraction with chloroform to remove colored impurities in U.S. Pat. No. 3,235,541; however, the process of this patent entails a pretreatment of the cellulose-derived pyrolysis oil and is encumbered by the fact that chloroform is highly toxic. After the chloroform extraction, the aqueous solution is concentrated to a syrup that is dissolved in acetone, and levoglucosan is isolated as a pure crystalline compound from the acetone solution after filtration and recrystallization.
Starch-containing feedstocks are utilized to provide levoglucosan from pyrolysis oils by treating the starch containing feedstocks with chemicals such as sulfur dioxide, calcium chloride and calcium acetate in U.S. Pat. No. 3,478,012; however the process of this patent necessitates pretreatment of the feedstocks before pyrolysis.
U.S. Pat. No. 3,309,356 is directed to a process for separating levoglucosan and carbohydrate acids; however, this patent pertains to the isolation of levoglucosan from pyrolysis oils that contain phenolics (i.e., wood as feedstock). Organic solvents are used to extract the phenolics from the crude pyrolysis oils, the extracted aqueous solution is dried azeotropically with methyl isobutyl ketone and the resulting organic solution is filtered to obtain levoglucosan from the filtrate. No data on the purity of the levoglucosan is provided.
A process for separating levoglucosan and carbohydrate-derived acids from aqueous mixtures is described in U.S. Pat. No. 3,374,222. In this process, after the pre-extraction of phenolics, the aqueous solution is treated with basic metal salts to precipitate polymeric carbohydrate-derived acids that are present in the pyrolysis oil. The precipitated materials are then removed through filtration to obtain a filtrate of an aqueous solution from which levoglucosan is isolated after elution through a cation exchange column.
There is a need extant in the art of producing levoglucosan to develop an efficient method for providing a high yield of pure, crystal line levoglucosan without subjecting pyrolysis oils from feedstock to highly toxic substances even when the pyrolysis oils contain low amounts of levoglucosan, so that levoglucosan can be subsequently converted into components of fast-curing adhesives.